Engine won't decelerate on it's own

[Melnickta]

I have driven my truck a couple of times in the past several days and am experiencing this problem:

The engine cranks and initially idles fine. The problem that I’m having is that once I press on the accelerator, the truck wants to stay at that speed/rpm. Even when I want to decelerate, I have to apply the brakes, and the truck still remains at whatever rpm it was running prior to me braking.

If at all possible, I would like to attempt to fix this myself (unless it involves rebuilding a carburetor). Any ideas what this could be and what the fix is?

Any help is appreciated.